In an on-camera interview with Fairfax Media's national Canberra bureau chief, Tim Lester, Senator Conroy dismissed the torrent of criticism directed at his policy as "misleading information" spread by "an organised group in the online world".

Asked what percentage of all of the nasty material on the internet his filters would block, Senator Conroy dodged the question, responding that his filters were "100 per cent accurate - no overblocking, no underblocking and no impact on speeds".

But Mark Newton, an engineer with ISP internode, said: "Censorship will not catch a single pedophile, will not cause a single image to disappear from the internet, will not protect a single child."

Senator Conroy also brushed aside concerns from leading academics and technology companies that the plan to block a blacklist of "refused classification" (RC) websites for all Australians was an attempt to shoe-horn an offline classification model into a vastly different online world.

"Why is the internet special?," he asked, saying the net was "just a communication and distribution platform".

"This argument that the internet is some mystical creation that no laws should apply to, that is a recipe for anarchy and the wild west. I believe in a civil society and in a civil society people behave the same way in the physical world as they behave in the virtual world."

Newton said this was a "gross oversimplification", pointing out that Australia Post and Telstra's telephone network were also distribution platforms but were not censored.

"Why should the internet, a distribution platform for all manner of intangibles, be censored as if it was a movie theatre? It makes no sense, the model doesn't fit," he said.

The Greens communications spokesman Scott Ludlam was also quick to ridicule Senator Conroy, saying books and films were distinctly different because they are "dicreet, physical packages of content", whereas the internet is dynamic and has "a trillion web pages already indexed and an unknown amount more added every day".

"To characterise sustained opposition by individuals and groups as diverse as EFA, Google, SAGE, Yahoo, Save the Children, Reporters without Borders, Justice Kirby, Choice Magazine, leading online academics and industry associations and the United States Department of State as 'an organised group in the online world' is a remarkably naive misreading of how unpopular this proposal is," Senator Ludlam said.

University of Sydney associate professor Bjorn Landfeldt said the difference between submitting a book for classification and having an organisation classifying and blocking websites without anyone's knowledge was that, in the book case, "it is well known that the book was censored and there can be a debate about the correctness of the decision".

Landfeldt said it was true that the filter system would block all websites it was told to block but the trillions of pages on the internet means the government will not make the internet a safe place for children and will only be able to stop access to "a small minority" of web pages.

Senator Conroy said the aim of his policy was to "ensure that particularly children ... don't stumble across this material", which he described as being child pornography, bestiality, extreme violence and pro-rape websites.

He neglected to address widespread concerns that the "refused classification" rating also applies to sexual health discussions, euthanasia material such as the Peaceful Pill Handbook, historical war footage and instructions in minor crimes such as graffiti.

Senator Conroy admitted that his filters would not do anything to stop the spread of child pornography on peer-to-peer file sharing networks, and that they will "slow down the internet" if applied to high-volume sites such as YouTube, Facebook and Wikipedia.

He mentioned he was in discussions with Google over a way for the company to apply the filter to YouTube but Google has already rejected these requests.

"If we know there are 355 websites today that have child pornographic images on it, should we say well we're not going to do anything about it?," he said.

Colin Jacobs, spokesman for the online users' lobby group Electronic Frontiers Australia, said this comment ignored evidence that the overwhelming majority of child pornography was traded in others ways such as by peer-to-peer. It also ignored the fact that anyone who wanted to bypass the filters could do so quite easily.

Senator Conroy has been on the attack against Google after the search giant issued a withering critique of his policy. After questioning the company's credibility in an ABC Radio interview on Monday night, he fired off another broadside in yesterday's interview.

He said Google already censored more material than the Rudd Government was proposing to block with its filters, pointing to its blocking of R-rated and X-rated material on YouTube and its censorship of search results in Thailand that are critical of the Thai king.

"Google are welcome to their view but Google have got to be prepared to be consistent," said Senator Conroy.

Jacobs said suggesting that enforcing YouTube's terms of service was equivalent to state-sponsored censorship was "at best misleading". Senator Ludlam said Senator Conroy's attacks on Google were "a deliberate misdirection of the debate", while Jacobs said they "smack of a personal vendetta".

Senator Conroy also rejected concerns that the government was creating a new mandatory censorship mechanism that would be prone to abuse by future governments.

"I think in Australia we have a vibrant democracy and anyone who wanted to try to expand beyond existing banned material - RC - would have one hell of a fight on the floor of Parliament," he said.

Asked whether it was a fact that the blacklist, a catalogue of some of the worst websites, was likely to leak at some time in the future, as has occurred in a number of other countries, Senator Conroy responded: "so the alternative is just to leave them out there and do nothing?".

He said he realistically would not expect to see legislation enabling the filters to be introduced before the second half of the year, after which it would "go through an open and transparent consultative process".

"For $44 million, we're buying ourselves an initiative which will have no measurable impact whatsoever," Senator Ludlam said.

"In exchange, we establish the architecture for future governments to abuse the loose and undefined 'RC' category to add a creeping range of material to the list. Once this architecture is established, the idea that its scope won't be expanded by future governments is a gamble we don't believe we should take."